Electric heating unit



Oct. 25, 1966 R. H. sTEGER ELECTRIC HEATING UNIT imi,

3W WQ' AGENT United States Patent O 3,281,750 ELECTRIC HEATING UNIT Robert Hugo Steger, 703 Waldburgstrasse 29, Boblingen, Germany Filed Oct. 8, 1964, Ser. No. 402,472 Claims priority, application Germany, Oct. 30, 1963, st 21,254 8 Claims. (Cl. 338-253) My present invention relates to a heating unit adapted to be used, with or without a juxtaposed reflector, as an emitter of thermal radiation and/or as a means for heating a surrounding, preferably gaseous, medium.

Heating units of this type, e.g. as employed `in space or air heaters, often have elongated tubular housings accommodating |one or more elongated heating elements, such as resistance coils. If the housing consists of refractory material, its poor thermal conductivity irnpedes the transmission of heat from the coil or coils to the surrounding medium inasmuch `as the housing must have an appreciable wall thickness for mechanical reasons. If, on the other hand, the housing is metallic, the problem of insulation creates difficulties.

It is, therefore, an important object of my present invention to provide an improved heating unit of the character described which eliminates the aforestated drawbacks and combines mechanical rigidity and compactness with operational safety and high thermal efficiency.

A more parti-cular object of the invention is to provide a unit of this description 1incorporating a plurality of heating elements, safely insulated from one another, whereby the rate of heat generation may be varied through selective connection of all or Iless than all the heating elements to an external power source. It is also an object of my invention to provide a heating unit of this type Whose housing and heating-coil support can be made from readily moldable ceramic material.

I have found, in accordance with this invention, that the above objects lcan be realized by the provision of a housing in the form of an elongated s-olid body of refractory insulating material, this body being formed with a longitudinally extending, eccentrically disposed cylindrical channel for each heating coil. In a multicoil heater, m-ore speciicaly, these channels are offset from the centerline of the cylindrical or otherwise centrally symmetrical body in such a way that the channel axes are equispaced from the centerline of the body and the channels themselves approach the outer periphery of the body to within a fraction of their own diameter, thus providing a region of reduced wall thickness preferably equal to approximately the channel radius. In order to extend this region of reduced Wall thickness and thereby to lower still further the thermal resistance of the body while also increasing its radiant surface, the body may be externally provided with longitudinal flutes which a-re interspersed with the locations of the -channels and define a scalloped body profile, each scallop (and therefore each zone of minimum thickness) encompassing an arc of substantially 180 around a respective channel.

For the purpose of more securely holding the heating coils in position within their channels, especially if the body is to be arranged vertically, I provide-*pursuant to still another feature of this invention--a granular filler to -occupy the interior of each coil, this filler consisting of an insulating material having about the same thermal coefficient of expansion as the material -of the body itself to avoid the occurrence of objectionable thermal stresses. The requirement of equal coefficient of expansion is, of course, best me-t if the filler consists of a comminuted substance of the same composition as the channeled body. It will be apparent that this Ifilling of the voids Within and between the turns of the coils, which are inserted with close fit int-o the channels, further strengthens the solid body mechanically; this is yof particular importance where the body has extensive regions of reduced wall thickness, as with the scalloped profile described above, but

can of course be used as well with bodies of cylindrical configuration.

The conduct-ors needed for the selective or concurrent energization of the several heating elements are advantageously led out at either or both ends of the elongated body. These ends, according to a further feature of the invention, are axially recessed and overlain by -respective mounting caps of insulating material which form passages for the conductors and are secured to the body by an adhesive mass, such as a layer of thermosetting resin, received in Ithese recesses. This provides a firm, fluidt'ight and dirtproof seal for the channels containing the heating coils.

The above and other objects and features of my invention will become more fully apparent from the following detailed description Aof certain embodiments, reference being made to the accompanying drawing in which:

FTIG. l is a top plan view of 4a heating unit embodying the invention;

FIG. 2 is a cross-sectional view taken on the line II- II of FIG. 1;

FIG. 3 is a plan view similar to FIG. l, showing a modied heating unit according to the invention;

FIG. 4 is a cross-sectional view taken on the line of IV- -IV of FIG. 3;

FIG. 5 is a top view of a mounting cap adapted to be used with the unit of either FIGS. 1 and 2 or FIGS. 3 and 4; and

FIG. 6 is a cross-sectional view taken on the line VI- VI of FIG. 5.

In FIGS. l and 2 I have shown a heating unit (without end caps) comprising a cylindrical lbody 1 of ceramic material, e.g. Alundum, formed with an annular array of cylindrical channels 4 which accommodate respective heating coils 2 (shown only in part). The cylinder axes 5 of the channels 4 are equispaced from the centerline 3 of the body 1, so as to lie on the surface 6 of an imaginary circular cylinder. The ends 8 of body 1 constitute axially extending flanges which define recesses 7 communicating with the channels 4. These recesses are 4occupied by a thermosetting mass 9, such las an epoxy resin, which seals the channels against the entrance of dirt and moisture and is traversed by the conductors (not shown in FIGS. 1 and 2) leading to the individual heating coils 2. The mass 9 also serves to hold in position la mounting cap 21 as illustrated in FIGS. 5 and 6 and described in detail hereinafter. The channels 4 are all of the sa-me diameter, substantially less than the radius of cylindrical body 1, and are so spaced from the periphery 10 of body 1 that the region 11 of minimum wall thickness measures about half the channel diameter. Thus, the coils 2 will effectively radiate their heat through the body 1 to the outside along these regi-ons of reduced thickness.

FIGS. 3 and 4 show a generally similar heating unit with a centrally symmetrical elongated body 12 of scalloped profile, this body being formed with external flutes 13 between the channels 14. The flutes 13 alternate with regions 17 of reduced Wall thickness, corresponding approximately to half the channel diameter, which envelop the several channels over approximately half their peripheries. The heating coils 18 (only two shown) received in these channels thus radiate most of their thermal energy outwardly through the thin wall portions 17, the scalloping in addition increasing the radiating surface of the heating unit and thereby improving its thermal efficiency. Body 12 is again provided at its ends With axial recesses, here -designated 16, which are formed by scalloped lianges 15 conforming to the prole of the main body section. The recesses 16 are occupied by sealing material 20 of the -character described above; the layers 20 are transversed :by conductors 29, 30 connected to the coils 18.

In order to strengthen the body 12 and brace the coils 18 against collapse within the channels 14 into which they have been inserted with close it, I prefer to introduce `a granular filler 19 into the voids left within and between the turns of each coil as illustrated in FIG. 4. The iiller 19 advantageously consists of the same refractory material (e.g.. Alundum) as the body itself. Naturally, such filler could :also be used with the coils 2 of the preceding embodiment.

In FIGS. and 6 I have shown a mounting cap 21 adapted t-o be placed on either end of a heating unit according to this invention, the unit having been indicated in dot-dash lines at 22 in FIG. 6. The device 22 is, of course, representative of a unit according to either of the two embodiments described above.

Cap 21, which is adhesively secured to `an en'd of unit 22 by the corresponding sealing layer 9 or 20, advantageously consists of the same refractory material as the body of the unit itself. On its side 24 remote from the unit 22, cap 21 is formed with a boss 25 of partially frusto-conical shape which has flat faces 26 and is undercut at 27 to facilitate its suspension from a suitable holder not shown. Passages 28 in boss 25 accommodate leads 31 which extend from the several heating elements of unit 22 in the manner illustrated at 29 or 30 in FIG. 4.

My invention is, of course, not limited to the specific arrangements described and illustrated but may be embodied in various modications without departing from the spirit and scope ofthe appended claims.

Iclaim:

1. A heating unit comprising an elongated centrally symmetrical solid body of refractory insulating material provided with an annular array of longitudinally extending cylindrical channels of like diameters with axes equispaced from a centerline of said body, an elongated heating element inserted with close iit in each of lsaid channels, and conductor means extending from said heating elements outwardly, each of said channels approaching the outer periphery of said body to Within a fraction of the diameter of said channels, said body being externally formed with longitudinal flutes interspersed with t-he locations of said channels and defining a scalloped profile of substantially constant minimum Wall thickness extending over an angle of substantially 180 around each element.

2. A heating unit as defined in cl-airn 1, further comcomprising `sealing means for retaining said heating element in said channels, said sealing means comprises a layer of thermosetting material closing said channels at each end of said body.

3. A heating unit as defined in claim 2 wherein said body is provided at each end with an axial recess communicating with said channels, s-aid layer being received in said recess.

4. A heating unit is dened in claim 3 wherein said sealing means further comprises a mounting cap of refractory insulating material engaging each end of said .body and held in place thereon by said thermosetting material.

5. A heating unit as defined in claim 4 wherein said cap is provided with a central boss having at least one passage, each of said heating elements being provided with conductors passing through said layer and traversing said passage of said mounting cap on at least one end of said body.

' 6. A heating unit as defined in claim 1 wherein each of said heating elements is a coil received with close lit in its channel, further comprising a granular liller of insulating material occupying the interior of said coil, said filler having a thermal coefficient of expansion substantially equaling that of the refractory material of said body. n

7. A heating unit las deiined in claim 6 wherein said filler and said -body consist of the `same material.

8. A heating unit as defined in claim 1 wherein the wall thickness of said -body at the point -of closest approach of `its outer periphery to each channel is substantially one-half the diameter of said channels.

References Cited by the Examiner UNITED STATES PATENTS 1,255,326 2/19'18 Macnicol 338-233 X 1,463,005 7/1923 Dalton 338-261 1,982,885 y12/1934 Stupakoff 174-99 X 1,995,000 3/1935 Hyatt 219--335 X 2,448,669 9/1948 Green 219-335 X 2,508,512 5/1950 Grinde 219-229 2,538,808 1/1951 Swiss 219--238 2,727,120 12/ 1955 Boggs 219-274 2,957,154 10/1960 Strokes 219-553 X 3,113,284 12/1963 Van Inthoudt 338-274 ANTHONY BARTIS, Acting Primary Examiner. RICHARD M. WOOD, Examiner.

V. Y. MAYEWSKY, Assistant Examiner. 

1. A HEATING UNIT COMPRISING AN ELONGATED CENTRALLY SYMMETRICAL SOLID BODY OF REFRACTORY INSULATING MATERIAL PROVIDED WITH AN ANNULAR ARRAY OF LONGITUDINALLY EXTENDING CYLINDRICAL CHANNELS OF LIKE DIAMETERS WITH AXES EQUISPACED FROM A CENTERLINE OF SAID BODY, AN ELONGATED HEATING ELEMENT INSERTED WITH CLOSE FIT IN EACH OF SAID CHANNELS, AND CONDUCTOR MEANS EXTENDING FROM SAID HEATING ELEMENTS OUTWARDLY, EACH OF SAID CHANNELS APPROACHING THE OUTER PERIPHERY OF SAID BODY TO WITHIN A FRICTION OF THE DIAMETER OF SAID CHANNELS, THE BODY BEING EXTERNALLY FORMED WITH LONGITUDINAL FLUTES INTERSPERSED WITH THE LOCATIONS OF SAID CHANNELS AND DEFINING A SCALLOPED PROFILE OF SUBSTANTIALLY CONSTANT MINIMUM WALL THICKNESS EXTENDING OVER AN ANGLE OF SUBSTANTIALLY 180* AROUND EACH ELEMENT. 